Turkish Journal of Physics




We re-analysed the behaviour of coronal activity of the RS CVn-type binaries as a function of stellar and orbital parameters. Highly significant correlations were found between the x-ray luminosity L_x and the stellar radius R, the Roche lobe filling fraction \Gamma, and the Alfven radius RA. The correlations of L_x with the mass M, the absolute magnitude M_V, the surface gravity g, the Roche lobe filling fraction \Gamma, and the Alfven radius RA are likely to be due to correlations of these quantities with the stellar radius R. Surprisingly, no correlation of L_x on the color (B-V), the rotation velocity V_{rot}, and the Rossby number RO is observed. However, significant correlations were found between the mean surface x-ray flux F_x=L_x/R_c^2+R_h^2 with the orbital period P_{orb}, the rotation velocity V_{rot}, the Rossby number RO. The activity-radius (and radius dependent parameters: \Gamma, M, g, M_V, and RA) correlations are mostly disappear when the mean surface flux F_x is used as the activity measure. We think the radius R (infact the surface area 4 \pi R^2) in L_x-R correlation represents the filling area S of the active regions on the stellar surface. The L_x thus increases with increasing surface area 4 \pi R^2 (in fact with increasing S). Slightly decreasing trend of the surface flux with the evolution off the main sequence (age or R^2) can be understood in terms of the decreasing filling fraction (S/4 \pi R^2) of the active regions with age.

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